The present invention relates to a servo positioning apparatus which is especially suited for positioning rotary printing element in an impact printer.
Impact printers comprising rotary type elements are well known in the art. Especially advantageous are the so-called daisy wheel printers comprising type elements having type members provided at the ends of spokes extending from a central hub. The type members bear characters, numerals, symbols and the like which are to be printed, with each character or the like corresponding to a discrete rotational position of a motor shaft on which the type element is mounted.
In order to print a character, a computing means computes the number of motor shaft steps or increments from a present position to the position corresponding to the character to be printed, and the motor is energized with an amount of power corresponding to the position difference. The amount of power is progressively reduced to zero as the shaft reaches the desired position. The shaft and type element are stopped at the desired position and a hammer is driven to impact the type member against a sheet of paper through a ribbon for printing.
Thereafter, the number of steps from the present position to the position of the next character to be printed is computed and the motor energized in accordance with the new difference.
An apparatus of this type as thus far developed is limited in speed of operation by the fact that the computing means must compute the distance to the next printing position after the motor shaft and type element reached the desired position for printing the present character. The computing operation takes a significant amount of time, and the motor shaft cannot be driven until the computation is completed.